Recommended Read Lock Time (How hard can I push ReadHistoryData)?

[MikeDash]

Hi, we've been working on an application that uses the DDK to read data out of Geo SCADA.

It is based on @sbeadle example project Data Feeder Engine.  It is working very well and can pull large amounts of data very quickly.  We don't want to overwork Geo SCADA though, (it is easy to adjust how much time it reads and how long it then rests), is there a "recommend" maximum Disk Lock Time percentage (or other metric) that we can tune to?

From the log:

21-JUL-2022 23:55:53.182 47A0 [LUS] Lock usage, 65.4161%, averaged over last 15 minutes (dynamic updated)

Regards,

Mike

[JChamberlain1]

40% is the general rule of thumb target, but you can certainly go higher if the types of locks aren't blocking other access to the database for extended periods of time.

That 65% is total lock time, not just reads. So long as it's mostly short reads  that can be released(and if it is mostly your data feeder then it probably is), 65% is probably fine, because you aren't blocking other reads and writes can jump in when they need to. So long as you aren't seeing performance issues on your ViewX clients, I wouldn't worry too much about it.

It's worth having a look at the database locks breakdowns in server status, that will tell you if there's anything worth improving. Look for the highest % and longest individual locks, especially write locks.

Ideally no individual lock should be longer than 1s, and anything longer than 30s can start to disconnect clients, partners and drivers.